Sintered NdFeB is an anisotropic magnet produced by powder sintering. Generally, only blanks can be produced through sintering, and then through mechanical processing (such as wire cutting, slicing, grinding, etc.) to become magnets of various shapes. The sintering of sintered NdFeB refers to the need to heat the green body below the melting point of the powder matrix phase in order to further improve the performance and usability of the magnet, improve the contact properties between powders, increase the strength, and make the magnet have high-performance microstructural characteristics. temperature and keep it warm for a period of time.
Sintering is an extremely important process in sintered NdFeB, and all manufacturers and researchers attach great importance to it. The relative density of NdFeB powder compacts is generally 50% to 70%, and the porosity is generally 30% to 50%. The bonding between particles is all mechanical bonding, and the bonding strength is extremely low. If the molding pressure is very high, some of the particles that have been in contact with each other have already undergone elastic or plastic deformation. At this time, the sample is more likely to crack, and its microstructure is not enough to produce high magnetic properties.
During the sintering process of sintered NdFeB body, a series of physical and chemical changes will occur. First, the gas (including water vapor) adsorbed on the surface of the powder particles is eliminated, the evaporation and volatilization of organic matter (such as oil that may be stained during isostatic pressing or the added antioxidants and lubricants, etc.), the stress is eliminated, and the surface of the powder particles is Reduction of oxides, recovery and recrystallization of deformed powder particles.
Under certain temperature conditions, that is, when dynamics allow, the contact between powder particles will be from point to surface in order to reduce the surface area and surface energy. As the contact surface between particles expands, the green body begins to shrink and densify, becoming a sintered NdFeB. In short, sintering is the process in which the powder combination changes from green body to rough body.
